CN115536886A

CN115536886A - Polyester film and release film

Info

Publication number: CN115536886A
Application number: CN202210754073.4A
Authority: CN
Inventors: 竹上竜太; 伊藤忠; 宫宅一仁
Original assignee: Fujifilm Corp
Current assignee: Fujifilm Corp
Priority date: 2021-06-29
Filing date: 2022-06-28
Publication date: 2022-12-30
Also published as: TW202319243A; KR20230002085A

Abstract

The invention provides a polyester film and a release film, which can produce ceramic green sheets with suppressed generation of concave-convex defects when the release film obtained by using the polyester film after long-term storage is used for producing the ceramic green sheets. The polyester film of the present invention comprises in order: a particle-containing layer containing particles; a polyester substrate substantially free of particles; and a particle-free layer substantially free of particles, wherein a release layer is formed on a surface of the particle-free layer on a side opposite to the polyester substrate, and the particle-free layer is used for producing a release film, and the particle-free layer contains a non-polyester resin other than a polyester resin.

Description

Polyester film and release film

Technical Field

The present invention relates to a polyester film and a release film.

Background

Biaxially oriented polyester films are used in a wide range of applications from the viewpoints of processability, mechanical properties, electrical properties, dimensional stability, transparency, chemical resistance and the like. For example, a release film obtained by laminating a release layer on the surface of a biaxially oriented polyester film is used for producing a ceramic green sheet for producing a laminated ceramic capacitor.

For example, patent document 1 discloses a release film for producing a ceramic sheet, which is obtained by using a biaxially oriented polyester film having 2 or more layers as a base material, the base material having a surface layer a substantially free of particles and a surface layer B containing particles, laminating a release coating layer on the surface of the surface layer a, and laminating a smoothing coating layer on the surface of the surface layer B, the smoothing coating layer having a specific areal surface average roughness (Sa) and a maximum protrusion height (P).

Patent document 1: japanese patent laid-open publication No. 2016-060158

With the recent increase in the capacity and size of ceramic capacitors, further thinning of ceramic green sheets is required. On the other hand, it is considered that the more the ceramic green sheet is made thinner, the more the surface shape of the release film has an influence on the performance of the ceramic green sheet. For example, if the release surface of the release film has an uneven shape, the uneven shape is transferred to the ceramic green sheet, and the thickness of the ceramic green sheet varies, which may degrade the performance of the ceramic capacitor product.

The present inventors have found that, when a release film obtained by forming a release layer on one surface of a polyester film after long-term storage of the polyester film for producing a release film as described in patent document 1 is used for producing a ceramic green sheet, at least one of fine recesses and projections may be formed in the ceramic green sheet, and there is room for improvement. Hereinafter, the minute concave and convex portions are collectively referred to as "concave-convex defect".

Disclosure of Invention

In view of the above circumstances, an object of the present invention is to provide a polyester film and a release film which can produce a ceramic green sheet with suppressed occurrence of concave-convex defects when a release film obtained by using a polyester film after long-term storage is used for producing a ceramic green sheet.

As a result of intensive studies to solve the above problems, the present inventors have found that a desired effect can be obtained when a polyester film is used which comprises a particle-containing layer containing particles, a polyester base material containing substantially no particles, and a particle-free layer containing substantially no particles and containing a non-polyester resin other than a polyester resin in this order, and have completed the present invention.

That is, the present inventors have found that the above problems can be solved by the following configuration.

[1]

A polyester film having in order:

a particle-containing layer containing particles;

a polyester substrate substantially free of particles; and

a particle-free layer substantially free of particles,

a release layer is formed on the surface of the particle-free layer on the side opposite to the polyester substrate to produce a release film,

the particle-free layer contains a non-polyester resin other than the polyester resin.

[2]

The polyester film according to [1], wherein,

the release film is used for manufacturing a ceramic green sheet.

[3]

The polyester film according to [1] or [2], wherein,

the non-polyester resin contained in the particle-free layer is at least one resin selected from the group consisting of acrylic resins, polyurethane resins, and olefin (olefin) resins.

[4]

The polyester film according to any one of [1] to [3], wherein,

the particle-containing layer contains a non-polyester resin other than a polyester resin.

[5]

The polyester film according to [4], wherein,

the non-polyester resin contained in the particle-containing layer is at least one resin selected from the group consisting of acrylic resins, polyurethane resins, and olefin resins.

[6]

The polyester film according to any one of [1] to [5], wherein,

when 100 different portions of the surface of the particle-free layer on the side opposite to the polyester base material were measured using an optical interferometer with a measurement area of 186. Mu. M.times.155. Mu.m per 1 portion, the total number of protrusions having a height of more than 50nm was 40 or less.

[7]

The polyester film according to any one of [1] to [6], wherein,

when 40 different sites on the surface of the particle-containing layer on the side opposite to the polyester base material were measured with a scanning electron microscope with a measurement area of 13 μm × 10 μm per 1 site, the total number of foreign substances having a diameter of more than 1 μm was 2 or less.

[8]

The polyester film according to any one of [1] to [7], wherein,

the maximum projection height Sp of the surface of the particle-free layer opposite to the polyester substrate is 1-30 nm, and

the particle-containing layer has a maximum projection height Sp of 10 to 1500nm on the surface opposite to the polyester base material.

[9]

The polyester film according to any one of [1] to [8], wherein,

the thickness of the particle-free layer and the thickness of the particle-containing layer are each 1 to 500nm.

[10]

The polyester film according to any one of [1] to [9], wherein,

the surface of the particle-containing layer on the side opposite to the polyester substrate has a surface free energy of 30 to 45mJ/m ² 。

[11]

The polyester film according to any one of [1] to [10], wherein,

the thickness of the polyester film is 40 μm or less.

[12]

A release film comprising the polyester film according to any one of [1] to [11] and a release layer provided on a surface of the particle-free layer on a side opposite to the polyester substrate.

[13]

The release film according to [12], wherein,

when 100 different portions of the surface of the release layer on the side opposite to the particle-free layer were measured using an optical interferometer with a measurement area of 186 μm × 155 μm per 1 portion, the total number of protrusions having a height of more than 50nm was 40 or less.

[14]

The release film according to [12] or [13], wherein,

the maximum protrusion height Sp of the surface of the particle-containing layer opposite to the polyester base material is 10-1500 nm, and

the maximum protrusion height Sp of the surface of the release layer opposite to the particle-free layer is 1 to 30nm.

Effects of the invention

According to the present invention, it is possible to provide a polyester film and a release film which can produce a ceramic green sheet in which generation of concave-convex defects is suppressed, when the release film obtained by using the polyester film after long-term storage is used for producing the ceramic green sheet.

Drawings

FIG. 1 is a cross-sectional view showing an example of the structure of the polyester film of the present invention.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiments, and can be implemented by appropriately changing the embodiments within the scope of the object of the present invention.

In the present specification, the numerical range expressed by the term "to" refers to a range including numerical values before and after the term "to" as a lower limit value and an upper limit value. In the numerical ranges recited in the present specification, the upper limit or the lower limit recited in a certain numerical range may be replaced with the upper limit or the lower limit recited in another numerical range recited in a stepwise manner. In addition, in the numerical ranges described in the present specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the values shown in the examples.

In the present specification, in the case where a plurality of substances corresponding to each component are present in the composition, the amount of each component in the composition refers to the total amount of the plurality of substances present in the composition, unless otherwise specified.

In the present specification, the term "step" includes not only an independent step, but also a step that can achieve a desired purpose of the step even when the step cannot be clearly distinguished from other steps.

In the present specification, a combination of two or more preferred embodiments is a more preferred embodiment.

In the present specification, the "longitudinal direction" refers to the longitudinal direction of a polyester film in the production of the polyester film, and has the same meaning as the "conveying direction" and the "machine direction".

In the present specification, the "width direction" refers to a direction orthogonal to the longitudinal direction. In the present specification, "orthogonal" is not limited to strict orthogonality, and includes substantial orthogonality. By "substantially orthogonal" is meant intersecting in the range of 90 ° ± 5 °, preferably 90 ° ± 3 °, more preferably 90 ° ± 1 °.

In the present specification, the "film width" refers to the distance between both ends of the polyester film in the width direction.

[ polyester film ]

The polyester film of the present invention (hereinafter, also referred to as "present film") has, in order: a particle-containing layer containing particles; a polyester substrate substantially free of particles; and a particle-free layer substantially free of particles, wherein a release layer is formed on a surface of the particle-free layer on a side opposite to the polyester substrate, and used for producing a release film. In the present film, the particle-free layer contains a non-polyester resin other than a polyester resin.

In the present film, the surface of the particle-containing layer opposite to the polyester substrate may be referred to as "1 st principal surface", and the surface of the particle-containing layer opposite to the polyester substrate may be referred to as "2 nd principal surface".

When a release film obtained by using the film after long-term storage of the film is used for producing a ceramic green sheet, a ceramic green sheet in which the occurrence of concave-convex defects is suppressed can be obtained. The reason for this is not clear, but is estimated to be as follows.

The polyester substrate contains impurities such as oligomers, and when the polyester film (or a release film obtained using the polyester film) is stored for a long period of time, projections due to the impurities may be deposited on the surface of the polyester substrate. Here, the oligomer is a low molecular weight by-product generated when the polyester resin is polymerized.

It is presumed that in the release film obtained by using such a polyester film, at least one of fine recesses and projections is formed on the release layer due to projections caused by impurities, and that in the ceramic green sheet formed on the surface of the release layer, concave-convex defects due to the fine recesses or projections of the release layer occur.

In order to solve this problem, the film has a particle-free layer containing a non-polyester resin on the surface on the side where the ceramic green sheet is formed. From this, it is presumed that precipitation of impurities on the surface of the polyester substrate and growth of impurities precipitated on the surface of the polyester substrate can be suppressed. As a result, it is considered that the generation of defects in the ceramic green sheet can be suppressed.

[ Structure ]

The structure of the present film will be explained with reference to the drawings.

FIG. 1 is a cross-sectional view showing an example of the structure of the present film. The polyester film 1 has a particle-containing layer 12, a polyester base 14 disposed on the particle-containing layer 12, and a particle-free layer 16 disposed on the polyester base 14.

The particle-containing layer 12 contains particles not shown, while the polyester base material 14 and the particle-free layer 16 contain substantially no particles.

The surface (1 st principal surface) of the particle-free layer 16 opposite to the polyester substrate 14 is the outermost layer of the polyester film 1 and is a surface for forming a release layer (described later). That is, after the polyester film 1 is produced, a release layer is laminated on the surface of the particle-free layer 16 opposite to the polyester substrate 14, thereby producing a release film having the polyester film 1 and the release layer.

The surface (the 2 nd principal surface) of the particle-containing layer 12 on the side opposite to the polyester base material 14 is the outermost layer of the polyester film 1.

The film of the present invention is not particularly limited as long as it has the particle-containing layer, the polyester base material, and the particle-free layer contains a non-polyester resin, and may have a configuration other than the configuration shown in fig. 1.

For example, in the structure shown in fig. 1, the particle-containing layer 12 is disposed in contact with the surface of the polyester substrate 14, but a primer layer or the like may be provided between the particle-containing layer 12 and the polyester substrate 14.

Hereinafter, each layer of the present film will be described in detail.

< particle-containing layer >

The particle-containing layer is a layer containing particles and is formed on one surface side of the polyester substrate. The surface of the particle-containing layer opposite to the surface facing the polyester base material constitutes the 2 nd main surface.

The film has a particle-containing layer, and thus can improve the transportability of a polyester film and a release film. More specifically, the winding quality (blocking resistance) can be improved, the occurrence of scratches and defects during conveyance can be suppressed, and the conveyance wrinkles during high-speed conveyance can be reduced.

The particle-containing layer may be provided directly on the surface of the polyester base material or may be provided on the surface of the polyester base material with another layer interposed therebetween, but is preferably provided directly on the surface of the polyester base material from the viewpoint of more excellent adhesion.

The particle-containing layer is not particularly limited as long as it contains particles, and preferably contains a non-polyester resin other than a polyester resin in addition to the particles. The particle-containing layer may contain an additive other than the particles and the non-polyester resin.

The particle-containing layer may be a crosslinked film crosslinked using a crosslinking agent described later.

(particles)

The average particle diameter of the particles contained in the particle-containing layer is not particularly limited, but is preferably 1 to 400nm, more preferably 10 to 200nm, and still more preferably 30 to 130nm from the viewpoint of more excellent transportability and the viewpoint of suppressing the transfer mark.

From the viewpoint of more excellent transportability and the viewpoint of suppressing the transfer mark, it is preferable that the average particle diameter of the particles contained in the particle-containing layer is 10 to 200nm (more preferably 30 to 130 nm), the thickness of the particle-containing layer is 1 to 200nm (more preferably 10 to 100 nm), and the average particle diameter of the particles is larger than the thickness of the particle-containing layer.

As the particles contained in the particle-containing layer, 1 kind of particles may be used alone, or 2 or more kinds of particles may be used.

In the case where the particle-containing layer contains 2 or more types of particles having different particle diameters, the particle-containing layer preferably contains at least 1 type of particles having an average particle diameter within the above range, and more preferably 2 or more types of particles having different particle diameters all have an average particle diameter within the above range.

Examples of the particles contained in the particle-containing layer include organic particles and inorganic particles. Among them, inorganic particles are preferable from the viewpoint of further improving the film winding quality, haze and durability (e.g., thermal stability).

As the organic particles, resin particles are preferable. Examples of the resin constituting the resin particles include acrylic resins such as polymethyl methacrylate (PMMA) resins, polyester resins, silicone resins, and styrene-acrylic resins. The resin particles preferably have a crosslinked structure. Examples of the resin particles having a crosslinked structure include divinylbenzene-crosslinked particles.

In the present specification, the acrylic resin refers to a resin containing a constituent unit derived from an acrylate or a methacrylate.

Examples of the inorganic particles include silica particles (silica particles, colloidal silica), titania particles (titania particles), calcium carbonate, barium sulfate, and alumina particles (alumina particles). Among the above, the inorganic particles are preferably silica particles from the viewpoint of further improving the haze and durability.

The shape of the particles is not particularly limited, and examples thereof include granular shape, spherical shape, cubic shape, spindle shape, scaly shape, aggregated shape, and indefinite shape. The agglomerated state means a state in which the particles are agglomerated 1 time. The shape of the aggregated particles is not limited, but is preferably spherical or indefinite.

The aggregated particles are preferably fumed silica particles. Examples of commercially available products that can be obtained include NIPPON AEROSIL co., and the AEROSIL series of ltd.

The non-aggregated particles are preferably colloidal silica particles. Examples of commercially available products that can be obtained include SNOWTEX series manufactured by Nissan Chemical Corporation.

From the viewpoint of transportability and coatability of the release layer, the content of particles in the particle-containing layer is preferably 0.1 to 30% by mass, more preferably 1 to 25% by mass, and still more preferably 1 to 15% by mass, relative to the total mass of the particle-containing layer.

The content of the particles is preferably 0.0001 to 0.01% by mass, more preferably 0.0005 to 0.005% by mass, based on the total mass of the polyester film.

(non-polyester resin)

The particle-containing layer preferably contains a non-polyester resin. Non-polyester resins can be used as binders.

The non-polyester resin contained in the particle-containing layer is not particularly limited as long as it is a resin other than a polyester resin, and examples thereof include an acrylic resin, a polyurethane resin, an olefin resin, a polyvinyl alcohol resin, and an acrylonitrile butadiene resin, and from the viewpoint of further improving the effects of the present invention, an acrylic resin, a polyurethane resin, or an olefin resin is preferable, and an acrylic resin or an olefin resin is more preferable.

Here, the solubility parameters (SP values) of the acrylic resin and the olefin resin deviate from those of the polyester resin. That is, since the compatibility between the acrylic resin and the olefin resin and the polyester resin is insufficient, impurities such as oligomers are not likely to be precipitated from the polyester substrate. It is thus presumed that projections due to impurities contained in the polyester base material are less likely to be generated on the surface of the particle-containing layer. Further, among the polyurethane resins, polyurethane resins having high hydrophobicity (that is, polyurethane resins having SP values sufficiently different from those of the polyester resins) can be inhibited from precipitating impurities such as oligomers from the polyester base material for the same reason as the acrylic resins and the olefin resins.

The particle-containing layer is preferably formed by coating an aqueous dispersion. From this viewpoint, the non-polyester resin contained in the particle-containing layer is preferably an acid-modified resin. The acid-modified resin is preferably a copolymer of (meth) acrylate and (meth) acrylic acid or an olefin resin having a carboxyl group, and more preferably an olefin resin having a carboxyl group.

Further, as the non-polyester resin contained in the particle-containing layer, from the viewpoint of easily adjusting the surface free energy of the particle-containing layer to a specific range described later, an acrylic resin, an olefin resin, or a polyurethane resin is preferable, an acrylic resin or an olefin resin is more preferable, and an acrylic resin is further preferable. The acrylic resin, olefin resin, and urethane resin are not particularly limited, and known resins can be used.

The olefin resin may be a resin containing a constituent unit derived from an olefin in the main chain. Since the main chain has an olefin structure, compatibility with the polyester resin becomes insufficient, and as a result, defect suppression during long-term storage can be further improved.

The olefin is not particularly limited, but is preferably an olefin having 2 to 6 carbon atoms (alkene), more preferably ethylene, propylene or hexene, and further preferably ethylene.

The olefin-derived constituent unit contained in the olefin resin is preferably 50 to 99 mol%, more preferably 60 to 98%, based on the entire constituent unit of the olefin resin.

As the olefin resin, an acid-modified olefin resin is preferable from the viewpoint that static electricity can be prevented when the release layer is applied. Examples of the acid-modified olefin resin include copolymers obtained by modifying the above-mentioned olefin resin with an acid-modifying component such as an unsaturated carboxylic acid or an acid anhydride thereof.

Examples of the acid-modifying component include acrylic acid, methacrylic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid, crotonic acid, and half-esters and half-amides of unsaturated dicarboxylic acids, and acrylic acid, methacrylic acid, maleic acid, and maleic anhydride are preferable from the viewpoint of dispersion stability of the resin.

Examples of the acidic group contained in the acid-modified olefin resin include a carboxyl group, a sulfo group and a phosphate group as the acidic group corresponding to the acid-modifying component, and a carboxyl group is preferable. The acidic group may form an acid anhydride, or may be neutralized with at least one selected from the group consisting of an alkali metal, an organic amine, and ammonia.

The acid-modified olefin resin may contain only 1 type of constituent unit having an acidic group, or may contain 2 or more types.

Examples of commercially available products of the acid-modified olefin resin include ZAIKKHENE series (registered trademark) such as ZAIKKHENE AC, A, L, NC and N (SUMITOMO SEIKA CHEMICALS CO., manufactured by LTD., CHEMICAL.), CHEMICEARL series (registered trademark) S100, S120, S200, S300, S650 and SA100 (manufactured by Mitsui Chemicals, inc.), HI-tech series (registered trademark) such as HI-tech S3121 and S3148K (manufactured by TOHO Chemical Industry Co., ltd.), ARROW BASE SE-1013, SE-1010, SB-1200, SD-1200, DA-1010, DB-4010 and ARROW BASE series (registered trademark) such as ARROW BASE Co., manufactured by TORIVT, HARDLEN AP-2, NZ-1004, NZ-315 (OBO-315), SUITORMO 1005, SUITORHOL, CHEMIC 407, and SUITORMO.

Further, the acid-modified olefin resins described in [0022] to [0034] of JP-A-2014-076632 can be preferably used.

The acrylic resin is a resin containing a constituent unit derived from a (meth) acrylate ester, and may be copolymerized with a vinyl monomer such as styrene. The acrylic resin is not particularly limited, and preferably contains a constituent unit derived from a (meth) acrylate having an alkyl group having 1 to 12 carbon atoms, and more preferably contains a constituent unit derived from a (meth) acrylate having an alkyl group having 1 to 8 carbon atoms.

From the viewpoint of preventing static electricity when the release layer is applied, the acrylic resin preferably has an acid-modifying component. The acrylic resin preferably contains a constituent unit derived from (meth) acrylic acid as an acid-modifying component. The (meth) acrylic acid may form an acid anhydride, or may be neutralized with at least one selected from the group consisting of an alkali metal, an organic amine, and ammonia.

When an aqueous dispersion of an acrylic resin is used for producing the particle-containing layer, an aqueous dispersion containing an acrylic resin and a dispersant can be preferably used.

The constituent unit derived from a (meth) acrylate ester contained in the acrylic resin is preferably 50 to 100 mol% based on the total constituent units of the acrylic resin.

The acid value of the acrylic resin is preferably 30mgKOH/g or less, more preferably 20mgKOH/g or less. The lower limit of the acid value is not particularly limited, but is, for example, 0mgKOH/g, but from the viewpoint of coating as an aqueous dispersion, preferably 2mgKOH/g or more.

When an acrylic resin having a solubility parameter (SP value) different from that of the polyester resin is used, the compatibility between the acrylic resin and the polyester resin is insufficient, and as a result, defect suppression during long-term storage can be further improved. Such an acrylic resin can be obtained, for example, by adjusting to satisfy at least one of the following conditions: the acid value is within the above range; and a constituent unit derived from a (meth) acrylate having an alkyl group having 1 to 12 carbon atoms. Among these, the acrylic resin is preferably obtained by adjusting the acid value to be within the above range and the constituent unit containing a (meth) acrylate derived from an alkyl group having 1 to 12 carbon atoms.

The urethane resin is not limited as long as it is a polymer having a urethane bond, and a known urethane resin such as a reaction product of an isocyanate compound and a polyol compound can be used.

In the case where an aqueous dispersion containing a polyurethane resin is used for producing the particle-containing layer, the aqueous dispersion preferably contains a polyurethane resin having an acidic group (for example, a carboxyl group), or contains a polyurethane resin and a dispersant. This improves the film formability of the particle-containing layer.

The polyurethane resin can be set to a desired SP value by adjusting at least one of the structure of the polyol compound as a raw material, the hydrophobicity or hydrophilicity of the polyol as a raw material, the structure of the isocyanate compound as a raw material, and the hydrophobicity or hydrophilicity of the isocyanate compound as a raw material, for example. By using the polyurethane resin adjusted to be hydrophobic in this manner, compatibility between the polyurethane resin and the polyester resin becomes insufficient, and as a result, defect suppression during long-term storage can be further improved.

Among the polyurethane resins, polyurethane resins having a polyester structure (polyester-based polyurethane resins) are preferred from the viewpoint of being hydrophobic and further capable of improving defect suppression during long-term storage.

Commercially available products of polyurethane include, for example, HYDRAN (registered trademark) AP-20, AP-40N and AP-201 (see above, DIC Corporation), TAKELAC (registered trademark) W-605, W-5030 and W-5920 (see above, mitsui Chemicals, inc.), SUPERFLEX (registered trademark) 210 and 130, and ELASTRON (registered trademark) H-3-DF, E-37 and H-15 (see above, DKS Co. Ltd.).

The particle-containing layer may contain 1 kind of non-polyester resin alone, or may contain 2 or more kinds of non-polyester resins.

From the viewpoint of further suppressing the uneven defects, the content of the non-polyester resin is preferably 30 to 99.8 mass%, more preferably 50 to 99.5 mass%, relative to the total mass of the particle-containing layer.

(additives)

The particle-containing layer may contain the above particles and an additive other than the non-polyester resin.

Examples of the additive to be contained in the particle-containing layer include a surfactant wax, a dispersant, an antioxidant, an ultraviolet absorber, a colorant, a reinforcing agent, a plasticizer, an antistatic agent, a flame retardant, a rust inhibitor, and a mold inhibitor.

The particle-containing layer preferably contains a surfactant from the viewpoint of improving smoothness of the region other than the region where the protrusions formed of the particles are present on the 2 nd main surface. By improving the smoothness of the region of the 2 nd main surface, the surface roughness of the 2 nd main surface is reduced by factors other than particles, and the maximum protrusion height Sp (described later) can be controlled within a desired range, thereby improving the effect of the present invention.

The surfactant is not particularly limited, and examples thereof include silicone surfactants, fluorine surfactants, and hydrocarbon surfactants. From the viewpoint of suppressing static electricity on the 2 nd main surface, a hydrocarbon surfactant is preferred.

The silicone surfactant is not particularly limited as long as it has a silicon-containing group as a hydrophobic group, and examples thereof include polydimethylsiloxane, polyether-modified polydimethylsiloxane, and polymethylalkylsiloxane.

Commercially available silicone surfactants include, for example, BYK (registered trademark) -306, BYK-307, BYK-333, BYK-341, BYK-345, BYK-346, BYK-347, BYK-348 and BYK-349 (manufactured by BYK Co., LTD, supra), KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-602, KF-6020, X-22-4515, KF-6011, KF-6012, KF-643 5 and KF-6017 (manufactured by Shin-Etsu Chemical Co., ltd., supra).

The fluorine-based surfactant is not particularly limited as long as it is a surfactant having a fluorine-containing group as a hydrophobic group, and examples thereof include perfluorooctanesulfonic acid and perfluorocarboxylic acid.

Commercially available fluorine-based surfactants include MEGAFACE (registered trademark) F-114, F-410, F-440, F-447, F-553, and F-556 (see DIC Corporation), and Surflon (registered trademark) S-211, S-221, S-231, S-233, S-241, S-242, S-243, S-420, S-661, S-651, and S-386 (AGC, manufactured by SESESEIMI CHEMICAL CO., LTD.).

In addition, as the fluorine-based surfactant, from the viewpoint of improving environmental compatibility, a surfactant derived from a material alternative to a compound having a linear perfluoroalkyl group having 7 or more carbon atoms, such as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), is preferable.

Examples of the hydrocarbon surfactant include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants.

Examples of the anionic surfactant include alkyl sulfate, alkyl benzene sulfonate, alkyl phosphate, and fatty acid salt.

Examples of the nonionic surfactant include polyalkylene glycol mono-or dialkyl ethers, polyalkylene glycol mono-or dialkyl esters, and polyalkylene glycol mono-alkyl ester/monoalkyl ether.

Examples of the cationic surfactant include primary to tertiary alkylamine salts and quaternary ammonium compounds.

Examples of the amphoteric surfactant include surfactants having both an anionic site and a cationic site in the molecule.

Commercially available products of anionic surfactants include, for example, RAPISOL (registered trademark) A-90, A-80, BW-30, B-90 and C-70 (manufactured by NOF CORPORATION), NIKKOL (registered trademark) OTP-100 (manufactured by Nikko Chemicals Co., ltd.), kohacool (registered trademark) 0N, L-40 and PHOSPHANOL (registered trademark) 702 (manufactured by TOHO Chemical In manufacturing Co., ltd.), BEAULIGHT (registered trademark) A-5000 and SSS (manufactured by Sanyo Chemical Industries, ltd.).

Commercially available products of the nonionic surfactant include, for example, NAROACTY (registered trademark) CL-95 and HN-100 (trade name, manufactured by Sanyo Chemical Industries, ltd.), risorex BW400 (trade name, manufactured by Kokyu Alcohol Kogyo Co., ltd.), EMALEX (registered trademark) ET-2020 (see above, NIHON EMULSI0N Co., manufactured by Ltd.), and SURINOL (registered trademark) 104E, 420, 440, 465, and Dynol (registered trademark) 604, 607 (see above, manufactured by Niss in Chemical Industry CO., ltd.).

When used together with the acid-modified resin, at least one of an anionic surfactant and a nonionic surfactant is preferable, and an anionic surfactant is more preferable, from the viewpoint of forming a coating layer having a smooth surface without inhibiting dispersion of the resin. That is, as the surfactant, an anionic hydrocarbon surfactant is more preferable from the viewpoint of improving surface smoothness.

From the viewpoint of further improving smoothness, the anionic hydrocarbon surfactant preferably has a plurality of hydrophobic end groups. The hydrophobic end group may be a part of a hydrocarbon group of the hydrocarbon surfactant. For example, a hydrocarbon surfactant having a hydrocarbon group having a branched structure at the end thereof has a plurality of hydrophobic end groups.

Examples of the anionic hydrocarbon surfactant having a plurality of hydrophobic end groups include sodium di-2-ethylhexyl sulfosuccinate (having 4 hydrophobic end groups), sodium di-2-ethyloctyl sulfosuccinate (having 4 hydrophobic end groups), and branched alkyl benzene sulfonate (having 2 hydrophobic end groups).

The surfactant may be used in 1 kind, or 2 or more kinds may be used simultaneously.

The content of the surfactant is preferably 0.1 to 10% by mass based on the total mass of the particle-containing layer, more preferably 0.1 to 5% by mass, and still more preferably 0.5 to 2% by mass, from the viewpoint of more excellent surface smoothness.

The paraffin wax is not particularly limited, and may be a natural wax or a synthetic wax. Examples of natural waxes include palm wax, candelilla wax, beeswax, montan wax, paraffin wax (Paraffin wax), and petroleum wax. Further, a lubricant described in [0087] of international publication No. 2017/169844 can be used.

The content of the paraffin is preferably 0 to 10 mass% with respect to the total mass of the particle-containing layer.

(thickness)

The particle-containing layer can be formed by, for example, applying a composition containing particles to one surface of a polyester substrate, and has a thickness of at most 1 μm or less.

The resin composition may be formed by extruding a polyester base material described later together with a resin for forming the particle-containing layer, and in this case, the particle-containing layer has a thickness of 1 to 10 μm in most cases.

The thickness of the particle-containing layer is preferably 1 to 500nm, more preferably 1 to 250nm, further preferably 10 to 100nm, and particularly preferably 20 to 100nm, from the viewpoint of the production suitability of the particle-containing layer and the reduction of haze.

The thickness of the particle-containing layer was an arithmetic average of the thicknesses at 5 points of the cut pieces obtained by preparing a cut piece having a cross section perpendicular to the main surface of the polyester film and measuring the cut piece with a Scanning Electron Microscope (SEM) or a Transmission Electron Microscope (TEM).

When the particle-containing layer is soft and it is difficult to stably produce a cross-sectional slice, measurement can be performed using a refractometer. Specifically, the film thickness of the particle-containing layer can be determined by fitting the measured reflectance spectrum to the film thicknesses and refractive indices of the particle-containing layer and the polyester base material.

The method for forming the particle-containing layer is described in detail in the "particle-containing layer forming step" described later.

< polyester substrate >

The polyester substrate is a film-like object containing a polyester resin as a main polymer component and substantially no particles. Here, the "main polymer component" means a polymer having the largest content (mass) of the entire polymers contained in the film.

"substantially no particles" means that, when the element derived from the particles is quantitatively analyzed by fluorescent X-ray analysis with respect to the polyester substrate, the content of the particles is 50 mass ppm or less, preferably 10 mass ppm or less, and more preferably detection limit or less with respect to the total mass of the polyester substrate. This is because, even if the particles are not positively added to the polyester base material, a contaminant component derived from a foreign substance or dirt attached to a production line or an apparatus in the production process of the raw material resin or the polyester base material may be peeled off and mixed into the polyester base material. Examples of the particles include particles contained in the particle-containing layer.

The polyester substrate may contain 1 kind of polyester resin alone or 2 or more kinds of polyester resins.

(polyester resin)

The polyester resin is a polymer having an ester bond in the main chain. The polyester resin is generally formed by polycondensing a dicarboxylic acid compound described later with a diol compound.

The polyester resin is not particularly limited, and a known polyester resin can be used. Examples of the polyester resin include polyethylene terephthalate (PET), polyethylene 2, 6-naphthalate (PEN), and copolymers thereof, and PET is preferable.

The intrinsic viscosity of the polyester resin is preferably 0.50dl/g or more and less than 0.80dl/g, more preferably 0.55dl/g or more and less than 0.70dl/g.

The polyester resin preferably has a melting point (Tm) of 220 to 270 ℃, more preferably 245 to 265 ℃.

The glass transition temperature (Tg) of the polyester resin is preferably from 65 to 90 ℃ and more preferably from 70 to 85 ℃.

The method for producing the polyester resin is not particularly limited, and a known method can be used. For example, the polyester resin can be produced by polycondensing at least one dicarboxylic acid compound with at least one diol compound in the presence of a catalyst.

Catalyst-

The catalyst used for producing the polyester resin is not particularly limited, and a known catalyst that can be used for synthesizing the polyester resin can be used.

Examples of the catalyst include alkali metal compounds (e.g., potassium compounds and sodium compounds), alkaline earth metal compounds (e.g., calcium compounds and magnesium compounds), zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, germanium compounds, and phosphorus compounds. Among them, a titanium compound is preferable from the viewpoints of catalytic activity and cost.

Only 1 kind of catalyst may be used, or 2 or more kinds may be used simultaneously. It is preferable to use at least one metal catalyst selected from the group consisting of potassium compounds, sodium compounds, calcium compounds, magnesium compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds and germanium compounds together with a phosphorus compound, and it is more preferable to use a titanium compound and a phosphorus compound together.

As the titanium compound, an organic chelate titanium complex is preferable. The organic chelate titanium complex is a titanium compound having an organic acid as a ligand.

Examples of the organic acid include citric acid, lactic acid, trimellitic acid, and malic acid.

As the titanium compound, the titanium compounds described in [0049] to [0053] of Japanese patent laid-open Nos. 5575671 can be used, and the contents of the above-mentioned publications are incorporated in the present specification.

Dicarboxylic acid compounds

Examples of the dicarboxylic acid compound include dicarboxylic acids such as aliphatic dicarboxylic acid compounds, alicyclic dicarboxylic acid compounds, and aromatic dicarboxylic acid compounds, and dicarboxylic acid esters such as methyl ester compounds and ethyl ester compounds of these dicarboxylic acids. Among them, aromatic dicarboxylic acids or aromatic dicarboxylic acid methyl esters are preferable.

Examples of the aliphatic dicarboxylic acid compound include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosanedioic acid, pimelic acid, azelaic acid, methylmalonic acid, and ethylmalonic acid.

Examples of the alicyclic dicarboxylic acid compound include adamantane dicarboxylic acid, norbornene dicarboxylic acid, cyclohexane dicarboxylic acid, and decahydronaphthalene dicarboxylic acid.

Examples of the aromatic dicarboxylic acid compound include terephthalic acid, isophthalic acid, phthalic acid, 1, 4-naphthalenedicarboxylic acid, 1, 5-naphthalenedicarboxylic acid, 2, 6-naphthalenedicarboxylic acid, 1, 8-naphthalenedicarboxylic acid, 4' -diphenyldicarboxylic acid, 4' -diphenyletherdicarboxylic acid, sodium 5-sulfoisophthalate, phenylindanedicarboxylic acid, anthracenedicarboxylic acid, phenanthrenedicarboxylic acid, and 9,9' -bis (4-carboxyphenyl) fluorenic acid.

Among them, terephthalic acid or 2, 6-naphthalenedicarboxylic acid is preferable, and terephthalic acid is more preferable.

The dicarboxylic acid compound may be used alone in 1 kind, or may be used in combination in 2 or more kinds. When terephthalic acid is used as the dicarboxylic acid compound, terephthalic acid may be used alone, or may be copolymerized with other aromatic dicarboxylic acids or aliphatic dicarboxylic acids such as isophthalic acid.

Diol compounds

Examples of the diol compound include aliphatic diol compounds, alicyclic diol compounds, and aromatic diol compounds, with aliphatic diol compounds being preferred.

Examples of the aliphatic diol compound include ethylene glycol, 1, 2-propanediol, 1, 3-propanediol, 1, 4-butanediol, 1, 2-butanediol, 1, 3-butanediol, and neopentyl glycol, and ethylene glycol is preferred.

Examples of the alicyclic diol compound include cyclohexanedimethanol, spiroglycol, and isosorbide.

Examples of the aromatic diol compound include bisphenol A, 1, 3-benzenedimethanol, 1, 4-benzenedimethanol and 9,9' -bis (4-hydroxyphenyl) fluorene.

The diol compounds may be used alone in 1 kind or in combination of 2 or more kinds.

Blocking agents

In the production of the polyester resin, an end-capping agent may be used as needed. By using the end-capping agent, a structure derived from the end-capping agent is introduced to the end of the polyester resin.

The end-capping agent is not limited, and a known end-capping agent can be used. Examples of the blocking agent include oxazoline compounds, carbodiimide compounds and epoxy compounds.

As the end-capping agent, reference may be made to the contents of [0055] to [0064] of Japanese patent application laid-open Nos. 2014-189002, the contents of which are incorporated herein by reference.

-manufacturing conditions-

The reaction temperature is not limited and may be appropriately set according to the starting materials. The reaction temperature is preferably 260 to 300 ℃ and more preferably 275 to 285 ℃.

The pressure is not limited and may be appropriately set according to the raw material. The pressure is preferably 1.33X 10 ^-3 ～1.33×10 ^- ⁵ MPa, more preferably 6.67X 10 ^-4 ～6.67×10 ^-5 MPa。

As a method for synthesizing the polyester resin, the methods described in [0033] to [0070] of Japanese patent No. 5575671 can be used, and the contents of the above-mentioned publications are incorporated in the present specification.

The polyester substrate is preferably a biaxially oriented polyester substrate.

"biaxial orientation" refers to the property of having molecular orientation in the biaxial direction. The molecular orientation was measured using a microwave transmission type molecular orientation meter (e.g., MOA-6004, oji Scientific Instruments Co., ltd.). The angle formed by the biaxial directions is preferably in the range of 90 ° ± 5 °, more preferably in the range of 90 ° ± 3 °, and still more preferably in the range of 90 ° ± 1 °.

The content of the polyester resin in the polyester base material is preferably 85 mass% or more, more preferably 90 mass% or more, further preferably 95 mass% or more, and particularly preferably 98 mass% or more, with respect to the total mass of the polymers in the polyester base material.

The upper limit of the content of the polyester resin is not limited, and can be appropriately set within a range of 100 mass% or less with respect to the total mass of the polymers in the polyester base material.

When the polyester substrate contains polyethylene terephthalate, the content of polyethylene terephthalate is preferably 90 to 100% by mass, more preferably 95 to 100% by mass, even more preferably 98 to 100% by mass, and particularly preferably 100% by mass, based on the total mass of the polyester resin in the polyester substrate.

The polyester substrate may contain components other than the polyester resin (for example, a catalyst, unreacted raw material components, particles, water, and the like).

From the viewpoint of controlling peelability, the thickness of the polyester substrate is preferably 100 μm or less, more preferably 50 μm or less, and further preferably 40 μm or less. The lower limit of the thickness is not particularly limited, but is preferably 3 μm or more, more preferably 10 μm or more, and further preferably 20 μm or more, from the viewpoint of improving strength and workability.

The thickness of the polyester substrate can be determined by subtracting the thickness of the particle-containing layer measured by the above-described method and the thickness of the particle-free layer measured by the below-described method from the thickness of the present film measured by the below-described method.

< layer containing no particles >

The particle-free layer is a layer substantially free of particles and is formed on the other surface side of the polyester substrate. The surface of the opposite side of the surface facing the polyester base material, which does not include the particle layer, constitutes the 1 st main surface.

"substantially no particles" means that, when the element derived from the particles is quantitatively analyzed by fluorescent X-ray analysis, the content of the particles is 50 mass ppm or less, preferably 10 mass ppm or less, and more preferably detection limit or less, with respect to the total mass of the particle-free layer. Examples of the particles in this case include particles contained in the particle-containing layer.

The particle-free layer is not particularly limited as long as it contains a non-polyester resin other than a polyester resin. The particle-free layer may contain an additive other than the polyester resin.

The particle-free layer may be a crosslinked film crosslinked by using a crosslinking agent described later.

(non-polyester resin)

The non-polyester resin contained in the particle-free layer is not particularly limited as long as it is a resin other than a polyester resin, and examples thereof include an acrylic resin, a polyurethane resin, an olefin resin, a polyvinyl alcohol resin, and an acrylonitrile butadiene resin, and from the viewpoint of further improving the effects of the present invention, an acrylic resin, a polyurethane resin, or an olefin resin is preferable, and an acrylic resin or an olefin resin is more preferable. When an acrylic resin or an olefin resin is used, protrusions due to impurities contained in the polyester base material are less likely to be generated on the surface of the particle-free layer from the viewpoint of the SP value of the polyester resin. Further, the polyurethane resin having high hydrophobicity among the polyurethane resins can also be inhibited from precipitating impurities such as oligomers from the polyester base material for the same reason as the acrylic resin and the olefin resin.

The olefin resin, the urethane resin, and the acrylic resin, including preferred embodiments thereof, may be the same as the olefin resin, the urethane resin, and the acrylic resin described as the non-polyester resin contained in the particle-containing layer.

The particle-free layer may contain an additive in addition to the non-polyester resin. Examples of the additives include surfactants, waxes, antioxidants, ultraviolet absorbers, colorants, reinforcing agents, plasticizers, antistatic agents, flame retardants, rust inhibitors, and mold inhibitors.

The surfactant may be the same as the surfactant contained in the particle-containing layer, including preferred embodiments thereof.

The thickness of the particle-free layer is at most 1 μm or less, preferably 1 to 500nm, more preferably 1 to 200nm, still more preferably 10 to 100nm, and particularly preferably 20 to 100nm. The thickness of the particle-free layer can be measured by the same method as the thickness of the particle-containing layer.

The particle-free layer is preferably disposed on the surface of the polyester substrate by inline coating. When the particle-free layer is provided by inline coating, it is preferably provided before or after the particle-containing layer forming step described later, or simultaneously with the particle-containing layer forming step. The polyester base material may be extruded together with a resin for forming a particle-free layer, and the particle-free layer may be provided on the surface of the polyester base material.

The present film may include layers other than the particle-containing layer, the polyester substrate, and the particle-free layer, but preferably has a layer structure composed of the particle-containing layer, the polyester substrate, and the particle-free layer.

[ Properties, etc. ]

Next, the physical properties and the like of the film will be described.

(surface free energy of the 1 st major surface)

The surface free energy of the 1 st principal surface (i.e., the surface on the opposite side of the polyester substrate without the particle layer) of the film is preferably 25 to 65mJ/m ² More preferably 30 to 45mJ/m ² More preferably 30 to 40mJ/m ² . The surface free energy of the first main surface 1 is set to 30 to 45mJ/m ² The effect of the present invention is more excellent because impurities such as oligomers are not easily precipitated from the polyester base material due to the deviation of the SP value from the polyester resin.

The surface free energy of the 1 st main surface can be adjusted by, for example, selecting the type of the non-polyester resin contained in the particle-free layer and additives.

The surface free energy of the 1 st main surface of the present film was obtained by the method described in the examples section below.

(surface free energy of the 2 nd principal plane)

The surface free energy of the 2 nd main surface (i.e., the surface of the particle-containing layer opposite to the polyester substrate) of the film is preferably 25 to 65mJ/m ² More preferably 30 to 45mJ/m ² More preferably 35 to 45mJ/m ² . The surface free energy of the 2 nd main surface is 30 to 45mJ/m ² In the range of (3), the oligomer produced from the polyester base material can be inhibited from being precipitated in a particulate state on the surface of the 2 nd main surface through the particle-containing layer. This makes it possible to prevent particles adhering to the surface of the 2 nd main surface from adhering to the 1 st main surface when the film is wound in a roll shape and stored.

The surface free energy of the 2 nd main surface can be adjusted by selecting a non-polyester resin, an additive, and the like, for example.

The surface free energy of the 2 nd main surface of the present film was obtained by the method described in the examples section below.

(maximum protrusion height Sp, surface roughness average Sa, number of local protrusions of No. 1 major surface)

From the viewpoint of smoothing the release layer, the 1 st main surface (i.e., the surface on the opposite side of the polyester substrate that does not include the particle layer) is preferably as smooth as possible. Specifically, the maximum protrusion height Sp of the 1 st main surface is preferably 1 to 60nm, more preferably 1 to 50nm, still more preferably 1 to 30nm, and particularly preferably 1 to 20nm.

The surface average roughness Sa of the 1 st main surface is preferably 0 to 10nm, more preferably 0 to 5nm, and still more preferably 0 to 2nm.

The number of local protrusions on the 1 st main surface is preferably 70 or less from the viewpoint of suppressing the occurrence of defects after long-term storage, and is preferably 40 or less, more preferably 20 or less, and still more preferably 10 or less from the viewpoint of smoothing the release layer. The lower limit of the number of local protrusions of the 1 st main surface is preferably 0.

The number of local protrusions on the 1 st main surface is the total number of protrusions having a height of more than 50nm, and is measured by the method described in the following example section.

The maximum protrusion height Sp, the surface average roughness Sa, and the number of local protrusions of the 1 st main surface can be adjusted by selecting the types of non-polyester resins and additives (surfactants, etc.) for forming the particle-free layer and forming a smooth coating layer without adding particles to the particle-free layer.

The maximum protrusion height sp, the surface average roughness Sa, and the number of local protrusions of the 1 st main surface of the present film were measured by the methods described in the examples section below.

The phrase "the surface average roughness Sa is 0nm" means that the surface average roughness Sa measured by the measurement method described later is not more than the measurement limit.

(maximum protrusion height Sp of No. 2 major surface, surface average roughness Sa, number of foreign matters)

When a release layer is formed on the 1 st principal surface of the present film to prepare a release film, the 2 nd principal surface of the present film corresponds to a transport surface which is the surface opposite to the release layer. The conveyance surface (the 2 nd main surface) is provided with a projection shape to improve conveyance performance, and on the other hand, when the projection shape is too large, a transfer mark may be formed on the peeling layer during storage of a roll for peeling a film. Therefore, from the viewpoint of suppressing the transfer mark on the surface of the release layer and the transportation property, the maximum projection height Sp of the 2 nd main surface is preferably within a predetermined range.

Specifically, the maximum protrusion height Sp of the 2 nd main surface is preferably 10 to 2300nm, more preferably 10 to 2000nm, still more preferably 10 to 1500nm, particularly preferably 10 to 500nm, most preferably 20 to 60nm.

From the viewpoint of suppressing the occurrence of defects after long-term storage, the number of foreign matters on the 2 nd main surface is preferably 7 or less, more preferably 4 or less, further preferably 2 or less, and particularly preferably 1 or less. The lower limit of the number of foreign matters on the 2 nd main surface is preferably 0.

The number of foreign matters on the 2 nd main surface is the total number of foreign matters having a diameter of more than 1 μm, and is measured by the method described in the following section of examples. The foreign substance is a particulate substance other than the particles contained in the particle-containing layer, and examples thereof include the oligomer.

From the viewpoint of further suppressing the imprint, the surface average roughness Sa of the 2 nd main surface is preferably 1 to 15nm, more preferably 1 to 10nm, and further preferably 3 to 8nm.

The maximum protrusion height Sp and the surface average roughness Sa of the 2 nd main surface can be adjusted by, for example, selecting the average particle diameter and the content of the particles contained in the particle-containing layer, the thickness of the particle-containing layer, and the types of the non-polyester resin and the additives (surfactant and the like) that can be contained in the particle-containing layer. In the case of forming the particle-containing layer by inline coating, the above adjustment can be performed more easily.

The maximum protrusion height Sp and the surface average roughness Sa of the 2 nd main surface were measured by the method described in the examples section below.

(thickness)

From the viewpoint of further excellent peelability, the thickness of the present film is preferably 100 μm or less, more preferably 50 μm or less, and further preferably 40 μm or less. The lower limit of the thickness is not particularly limited, but is preferably 3 μm or more, more preferably 5 μm or more, and further preferably 10 μm or more, from the viewpoint of excellent workability.

The thickness of this film was an arithmetic mean value of the thickness at 5 points measured by a continuous stylus thickness meter.

[ production method ]

As embodiment 1 of the present film production method, there is a method including: a biaxial stretching step of biaxially stretching an unstretched polyester substrate; a particle-containing layer forming step of forming a particle-containing layer containing particles; and a particle-free layer forming step of forming a particle-free layer substantially free of particles.

The biaxial stretching may be simultaneous biaxial stretching in which longitudinal stretching and transverse stretching are performed simultaneously, or sequential biaxial stretching in which longitudinal stretching and transverse stretching are performed in multiple stages of 2 stages or more. Examples of the form of the sequential biaxial stretching include longitudinal stretching → transverse stretching, longitudinal stretching → transverse stretching → longitudinal stretching, longitudinal stretching → transverse stretching, and transverse stretching → longitudinal stretching, preferably longitudinal stretching → transverse stretching.

The present production method includes, for example, a method including: an extrusion molding step of extruding a molten resin containing a raw material polyester resin into a film shape to form an unstretched polyester base material; a biaxial stretching step including a longitudinal stretching step of stretching an unstretched polyester base material in a transport direction to form a uniaxially oriented polyester base material and a transverse stretching step of stretching the uniaxially oriented polyester base material in a width direction to form a biaxially oriented polyester base material; a heat-setting step of heating and heat-setting a biaxially oriented polyester substrate; a heat relaxation step of heating and relaxing the polyester substrate heat-set in the heat setting step at a temperature lower than that in the heat setting step; a cooling step of cooling the polyester substrate thermally relaxed by the thermal relaxation step; a spreading step of spreading the heat-moderated polyester substrate in the width direction in the cooling step; a particle-containing layer forming step of providing a particle-containing layer on one surface of a polyester base material by an inline coating method using a particle-containing layer-forming composition containing particles; and a particle-free layer forming step of forming a particle-free layer on the other surface of the polyester substrate by an inline coating method using a composition for particle-free layer formation that does not substantially contain particles.

< extrusion Molding Process >

The extrusion molding step is a step of extruding a molten resin containing a raw material polyester resin into a film shape by an extrusion molding method to form an unstretched polyester substrate. The polyester resin as a raw material is the same as that described in the above (polyester resin) project.

The extrusion molding method is a method of molding a raw material resin into a desired shape by extruding a melt of the raw material resin using an extruder, for example.

Upon cooling, the melt extruded from the extrusion die was shaped into a film. For example, the melt can be formed into a film shape by bringing the melt into contact with a casting roll, cooling and solidifying the melt on the casting roll. In cooling the melt, it is preferable to blow air (preferably cold air) further to the melt.

< biaxial stretching Process >

The biaxial stretching step comprises: a longitudinal stretching step of stretching an undrawn polyester substrate in a transport direction (hereinafter, also referred to as "longitudinal stretching") to form a uniaxially oriented polyester substrate; and a transverse stretching step of stretching the uniaxially oriented polyester substrate in the width direction (hereinafter also referred to as transverse stretching) to form a biaxially oriented polyester substrate.

(longitudinal stretching Process)

The longitudinal stretching is performed by, for example, applying tension between 2 or more pairs of stretching rolls provided in the transport direction while transporting the unstretched polyester substrate in the longitudinal direction.

The stretch ratio in the longitudinal stretching step is appropriately set according to the application, and is preferably 2.0 to 5.0 times, more preferably 2.5 to 4.0 times, and still more preferably 2.8 to 4.0 times.

The stretching speed in the longitudinal stretching step is preferably 800 to 1500%/second, more preferably 1000 to 1400%/second, and further preferably 1200 to 1400%/second. Here, the "stretching speed" is a value represented by a percentage obtained by dividing the length Δ d in the transport direction of the polyester substrate stretched for 1 second in the longitudinal stretching step by the length d0 in the transport direction of the polyester substrate before stretching.

In the longitudinal stretching step, the unstretched polyester substrate is preferably heated. This is because longitudinal stretching is facilitated by heating.

(transverse drawing Process)

The transverse stretching step is a step of transversely stretching the uniaxially oriented polyester base material.

In the transverse stretching process, the polyester substrate is preferably preheated before the transverse stretching. By preheating the polyester substrate, the polyester substrate can be easily stretched in the transverse direction.

The stretching ratio in the width direction (transverse stretching ratio) of the uniaxially oriented polyester substrate in the transverse stretching step is not particularly limited, and is preferably larger than the stretching ratio in the longitudinal stretching step. The stretching ratio in the transverse stretching step is preferably 3.0 to 6.0 times, more preferably 3.5 to 5.0 times, and still more preferably 3.5 to 4.5 times.

When the transverse stretching step is performed in the stretching section of the stretching machine, the transverse stretching magnification is determined from the ratio (L1/L0) of the polyester substrate width L1 at the time of carrying out from the stretching section to the polyester substrate width L0 at the time of carrying in from the stretching section.

The stretching speed in the transverse stretching step is preferably 8 to 45%/second, more preferably 10 to 30%/second, and further preferably 15 to 20%/second.

< Heat setting step >

In the present production method, a heat setting step is preferably performed as a heat treatment for the polyester substrate stretched in the transverse direction stretching step.

In the heat setting step, the biaxially oriented polyester substrate obtained in the transverse stretching step can be heated and heat set. The shrinkage of the polyester substrate can be suppressed by crystallizing the polyester resin by heat setting.

The surface temperature (heat-setting temperature) of the polyester substrate in the heat-setting step is not particularly limited, but is preferably lower than 240 ℃, more preferably 235 ℃ or lower, and further preferably 230 ℃ or lower. The lower limit is not particularly limited, but is preferably 190 ℃ or higher, more preferably 200 ℃ or higher, and still more preferably 210 ℃ or higher.

The heating time in the heat-setting step is preferably 5 to 50 seconds, more preferably 5 to 30 seconds, and still more preferably 5 to 10 seconds.

< thermal relaxation step >

In the heat relaxation step, it is preferable to heat the polyester substrate heat-set in the heat setting step at a temperature lower than that in the heat setting step to thereby perform heat relaxation. The residual stress of the polyester substrate can be relaxed by thermal relaxation.

The surface temperature (heat relaxation temperature) of the polyester substrate in the heat relaxation step is preferably a temperature lower by 5 ℃ or more, more preferably a temperature lower by 15 ℃ or more, further preferably a temperature lower by 25 ℃ or more, and particularly preferably a temperature lower by 30 ℃ or more than the heat setting temperature. That is, the thermal relaxation temperature is preferably 235 ℃ or lower, more preferably 225 ℃ or lower, still more preferably 210 ℃ or lower, and particularly preferably 200 ℃ or lower.

The lower limit of the thermal relaxation temperature is preferably 100 ℃ or more, more preferably 110 ℃ or more, and further preferably 120 ℃ or more.

< Cooling Process >

The present production method preferably includes a cooling step of cooling the polyester substrate having a moderate heat.

The cooling rate of the polyester substrate in the cooling step is not particularly limited, and from the viewpoint of reducing the thickness unevenness of the release layer laminated on the present film and further improving the coatability of the release layer, it is preferably more than 2000 ℃/min and less than 4000 ℃/min, more preferably 2000 to 3500 ℃/min, still more preferably more than 2200 ℃/min and less than 3000 ℃/min, and particularly preferably 2300 to 2800 ℃/min.

< extension step >

In the cooling step, it is also preferable to include a step of spreading the heat-moderated polyester substrate in the width direction.

The spreading ratio in the width direction of the polyester substrate in the spreading step, that is, the ratio of the width of the polyester substrate at the end of the cooling step to the width of the polyester substrate before the start of the cooling step is preferably 0% or more, more preferably 0.001% or more, and still more preferably 0.01% or more.

The upper limit of the expansion ratio is not particularly limited, but is preferably 1.3% or less, more preferably 1.2% or less, and further preferably 1.0% or less.

< particle-containing layer Forming step >

The production method preferably includes a particle-containing layer forming step of performing inline coating using a particle-containing layer forming composition containing particles (hereinafter also referred to as "composition B"). The particle-containing layer formed on one surface of the polyester base material in the particle-containing layer forming step is the same as the layer described in detail in the item < particle-containing layer >.

The particle-containing layer can be formed at any stage of the production process, and examples thereof include a method in which a coating film is formed on one surface of an unstretched or stretched polyester substrate, and dried as necessary.

First, a method for forming a particle-containing layer using composition B will be described.

The composition B can be prepared by mixing the particles contained in the particle-containing layer, a non-polyester resin and additives added as needed, and a solvent.

Examples of the solvent include water and ethanol.

The composition B may contain 1 kind of solvent alone or 2 or more kinds of solvents.

The content of the solvent is preferably 80 to 99.5% by mass, more preferably 90 to 99.0% by mass, based on the total mass of the composition B.

That is, the total content of the components other than the solvent (solid content) in the composition B is preferably 0.5 to 20% by mass, more preferably 1 to 10% by mass, based on the total mass of the composition B.

The particles, the non-polyester resin and the additives contained in the composition B, including preferred embodiments thereof, are described in detail in the item of the above < particle-containing layer >.

The content of each component in the coating liquid is preferably adjusted so that the content of each component with respect to the total mass of the solid components in the composition B is the same as the preferred content of each component with respect to the total mass of the particle-containing layer.

Composition B may also contain a crosslinking agent.

The crosslinking agent is not particularly limited, and a known crosslinking agent can be used.

Examples of the crosslinking agent include melamine compounds, oxazoline compounds, epoxy compounds, isocyanate compounds and carbodiimide compounds, and oxazoline compounds or carbodiimide compounds are preferable. Examples of commercially available products include CARBODILITE V-02-L2 (manufactured by Nisshihbo Co., ltd.) and EPOCROS K-2020E (NIPPON SHOKUBA CO., LTD.). For details of the epoxy compound, the isocyanate compound and the melamine compound, reference can be made to the descriptions of [0081] to [0083] of Japanese patent laid-open No. 2015-163457. The crosslinking agent described in [0082] to [0084] of the international publication No. 2017/169844 can also be preferably used. As carbodiimide compounds, reference can be made to the descriptions of [0038] to [0040] in Japanese patent laid-open publication No. 2017-087421.

As the oxazoline compound, carbodiimide compound and isocyanate compound, crosslinking agents described in [0074] to [0075] of the international publication No. 2018/034294 can be preferably used.

The content of the crosslinking agent is preferably 0 to 50% by mass based on the total mass of the solid components in the composition B.

In the case where the composition B contains a non-polyester resin, the composition B is preferably a latex in which particles of the non-polyester resin are dispersed in water. In this case, the average particle diameter of the particles of the non-polyester resin is preferably 10 to 1000nm, more preferably 20 to 500nm, and still more preferably 50 to 200nm.

If the average particle diameter of the particles of the non-polyester resin is 50nm or more, the number of local protrusions on the 2 nd main surface can be reduced, and therefore the effect of the present invention is more excellent. The composition B is excellent in coatability as long as the average particle diameter of the non-polyester resin is 200nm or less.

The average particle diameter of the particles of the non-polyester resin is a value (D50) of 50% diameter calculated from a volume average of particle size distribution measured by a laser diffraction/scattering particle size distribution measuring instrument ("LA-950", manufactured by HORIBA, ltd.).

The method for applying the composition B is not particularly limited, and a known method can be used. Examples of the coating method include a spray coating method, a slit coating method, a roll coating method, a blade coating method, a spin coating method, a bar coating method, and a dip coating method.

In the particle-containing layer forming step, an inline coating method of coating a coating liquid on one surface of a polyester substrate while conveying the polyester substrate is preferably applied. By applying the inline coating method, the heating time of the polyester substrate in the production process is shortened, and the thermal history is not required, so that the striped defect region can be reduced.

In the inline coating method, the polyester substrate of the coating composition B may be an unstretched polyester substrate or a uniaxially oriented polyester substrate, but is preferably a uniaxially oriented polyester substrate. That is, the particle-containing layer forming step is preferably a coating step performed between the longitudinal stretching step and the transverse stretching step. This is because the adhesiveness between the polyester base material and the particle-containing layer can be improved by stretching the uniaxially oriented polyester base material and the particle-containing layer in the transverse direction at the same time.

< Process for Forming particle-free layer >

The production method preferably includes a particle-free layer formation step of performing direct discharge coating using a particle-free layer formation composition (hereinafter, also referred to as "composition a") that does not substantially contain particles. The particle-free layer formed on the other surface of the polyester base material by the particle-free layer forming step is the same as the layer described in detail in the item of the above < particle-free layer >.

The particle-free layer may be formed at any stage of the production process, and examples thereof include a method in which a coating film is formed on the other surface of a polyester substrate which is not stretched or stretched, and dried as necessary.

The particle-free layer forming step is the same as the < particle-containing layer forming step > except that the composition a is used to form a particle-free layer on the other surface of the polyester base material.

The composition a can be prepared by mixing a non-polyester resin, additives and a solvent which are added as needed.

The solvent is as described in the item < particle-containing layer forming step > above, including the preferred embodiments.

The non-polyester resin and the additive contained in the composition a are described in detail in the item of the above < particle-free layer >, including preferred embodiments thereof.

The content of each component in the coating liquid is preferably adjusted so that the content of each component with respect to the total mass of the solid components in the composition a is the same as the preferred content of each component with respect to the total mass of the particle-free layer.

Composition a may also contain a crosslinking agent. The crosslinking agent contained in composition a is the same as the crosslinking agent contained in composition B, including the preferred embodiments.

Composition a is preferably a latex in which particles of a non-polyester resin are dispersed in water. In this case, the preferable range of the average particle diameter of the particles of the non-polyester resin is the same as that of the particles of the non-polyester resin in the above composition B.

The production method may further comprise a winding step of winding the biaxially oriented polyester substrate obtained through the above-mentioned steps to obtain a rolled biaxially oriented polyester substrate.

The transport speed of the polyester substrate in each step other than the longitudinal stretching step in the present production method is not particularly limited, and when the transverse stretching step, the heat setting step, the heat relaxing step, the cooling step, and the stretching step are performed, from the viewpoint of productivity and quality, it is preferably 50 to 200 m/min, and more preferably 80 to 150 m/min.

< other embodiment of the method for producing a thin film >

As embodiment 2 of the present film production method, there is a method comprising: a step (laminate X forming step) of extruding a molten resin containing a polyester resin as a raw material for forming an unstretched polyester base material together with a particle-containing molten resin containing particles for forming a particle-containing layer and a non-polyester resin to form a laminate X in which the unstretched polyester base material and the particle-containing layer are laminated; and a particle-free layer forming step of forming a particle-free layer substantially free of particles by coating.

The raw material polyester resin, particles, and non-polyester resin are as described in embodiment 1.

The method of co-extrusion in the laminate X forming step can be the same as the extrusion molding step in embodiment 1, except that the particle-containing molten resin is used together with the molten resin.

The respective steps such as the biaxial stretching step, the heat setting step, the heat relaxing step, the cooling step, and the expanding step described in embodiment 1 are preferably performed using the laminate X.

The particle-free layer forming step can be the same as the particle-free layer forming step in embodiment 1.

As embodiment 3 of the present film production method, there is a method comprising: a step of extruding a molten resin containing a polyester resin as a raw material for forming an unstretched polyester base material, a particle-containing molten resin containing particles for forming a particle-containing layer and a non-polyester resin, and a non-polyester molten resin containing a non-polyester resin for forming a particle-free layer together to form a laminate Y in which the particle-free layer, the unstretched polyester base material, and the particle-containing layer are laminated in this order (laminate Y forming step).

The method of co-extrusion in the laminate Y forming step can be the same as the extrusion molding step in embodiment 2, except that the particle-containing molten resin and the non-polyester molten resin are used together with the molten resin.

The respective steps such as the biaxial stretching step, the heat setting step, the heat relaxing step, the cooling step, and the stretching step described in embodiment 1 are preferably performed using the laminate Y.

In the method for producing the film, the contents of [0113] to [0169] of the international publication No. 2020/241692 are referred to, and the contents are incorporated in the present specification.

In the present method for producing a thin film described specifically above, a combination of 2 or more preferred embodiments is a more preferred embodiment.

[ Release film ]

The film can be used for producing a release film. More specifically, a release film having the present film and a release layer disposed on the 1 st principal surface of the present film can be produced by providing a release layer on the 1 st principal surface of the present film (the surface on the opposite side of the polyester substrate from which the particle layer is not included).

The release layer contains at least a resin as a release agent. The resin contained in the release layer is not particularly limited, and examples thereof include silicone resins, fluororesins, alkyd resins, acrylic resins, various paraffins, and aliphatic olefins, and silicone resins are preferred from the viewpoint of releasability of the ceramic green sheet.

The silicone resin refers to a resin having a silicone structure in a molecule. Examples of the silicone resin include curable silicone resins, silicone graft resins, and modified silicone resins such as alkyl modification, and reactive curable silicone resins are preferred.

Examples of the reactive curable silicone resin include addition reaction type silicone resins, condensation reaction type silicone resins, and ultraviolet or electron beam curable type silicone resins. Among them, an addition reaction type silicone resin having low-temperature curability, or an ultraviolet or electron beam curing type silicone resin is preferable because a release layer can be formed at a low temperature.

Examples of the addition reaction type silicone resin include resins obtained by reacting polydimethylsiloxane having a vinyl group introduced at a terminal or a side chain thereof with hydrogenated diene siloxane using a platinum catalyst and curing the reaction product.

Examples of the condensation-reaction-type silicone resin include resins having a three-dimensional crosslinked structure formed by condensation reaction of polydimethylsiloxane having OH groups at the terminals and polydimethylsiloxane having H groups at the terminals using an organotin catalyst.

Examples of the ultraviolet-curable silicone resin include resins that are crosslinked by the same radical reaction as in the case of crosslinking silicone rubber, resins that are photocured by introducing an unsaturated group, resins that are crosslinked by decomposing an onium salt with ultraviolet light or an electron beam to generate a strong acid and cleaving an epoxy group, and resins that are crosslinked by an addition reaction of a thiol and a vinyl siloxane. More specifically, acrylate-modified polydimethylsiloxanes and glycidyloxy-modified polydimethylsiloxanes are mentioned.

The release layer may contain an additive in addition to the above-mentioned resin. As the additives, additives such as a light release additive and a heavy release additive for adjusting the release force, an adhesion improver, a curing agent (crosslinking agent), and an antistatic agent may be added.

The resin contained in the release layer may be used alone in 1 kind, or may be used in 2 or more kinds.

The content of the resin in the release layer is preferably 50 to 99% by mass, more preferably 60 to 98% by mass, based on the total mass of the release layer. The remainder of the release layer other than the resin may be at least one of the above-described additives and residues such as a solvent and a catalyst contained in the release layer-forming coating liquid for forming the release layer.

The thickness of the release layer is not particularly limited as long as it is set according to the purpose of use, but is preferably 0.005 to 2.0. Mu.m, more preferably 0.05 to 1.0. Mu.m, from the viewpoint of excellent balance between release performance and smoothness of the surface of the release layer.

(surface free energy of the Release surface)

From the viewpoint of antistatic properties when the release film is wound, the surface free energy of the surface of the release layer opposite to the side not containing the particles (also referred to as release surface) is preferably 30mJ/m ² More preferably 1 to 30mJ/m ² More preferably 10 to 30mJ/m ² 。

The surface free energy of the release surface of the release layer can be adjusted by the type of the resin forming the release layer and the additive.

(maximum protrusion height Sp of peeled surface, surface average roughness Sa, local protrusion number)

From the viewpoint of smoothing the functional layer such as a ceramic green sheet formed on the release layer, the release surface is preferably as smooth as possible. Specifically, the maximum protrusion height Sp of the release surface is preferably 1 to 60nm, more preferably 1 to 40nm, and still more preferably 1 to 30nm.

The surface average roughness Sa of the release surface is preferably 0 to 10nm, more preferably 0 to 5nm.

The number of local protrusions on the release surface is preferably 70 or less, and from the viewpoint of improving the smoothness of the release surface, the number is preferably 40 or less, more preferably 20 or less, and still more preferably 10 or less. The lower limit of the number of local protrusions on the release surface is preferably 0.

The maximum protrusion height Sp, the surface average roughness Sa, and the number of local protrusions of the release layer can be adjusted by, for example, not adding particles to the release layer when the release layer is provided, and selecting a resin and an additive for forming the release layer. The maximum protrusion height Sp, the surface average roughness Sa, and the number of local protrusions of the particle-free layer can be adjusted within the above ranges.

The maximum protrusion height Sp, the surface average roughness Sa, and the number of local protrusions of the peeled surface were measured by the methods described in the examples section below.

The method for providing a release layer on the 1 st main surface of the present film is not particularly limited, and the following methods may be mentioned: a release layer-forming coating liquid in which a release agent is dissolved or dispersed in a solvent is applied to the 1 st main surface of the present film, and the solvent is removed by drying, and a cured product is formed by heating or irradiating light as necessary.

The release layer is preferably a cured product cured by light (e.g., ultraviolet light) or heat.

The coating method of the coating liquid for forming the release layer is not particularly limited, and a known method can be used. Examples of the coating method include a spray coating method, a slit coating method, a roll coating method, a blade coating method, a spin coating method, a bar coating method, and a dip coating method.

The heating temperature for forming the release layer is preferably 180 ℃ or lower, more preferably 150 ℃ or lower, and still more preferably 120 ℃ or lower. The lower limit is not particularly limited, and may be 60 ℃ or higher.

The coating liquid for forming a release layer contains the resin and the solvent, and may contain at least one of the additive and the catalyst for curing the resin, if necessary. The coating liquid for forming a release layer can be prepared by mixing these components.

Examples of the solvent include water and organic solvents such as toluene, methyl ethyl ketone, ethanol, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether, and organic solvents are preferred.

The coating liquid for forming a release layer may contain 1 kind of solvent alone, or may contain 2 or more kinds of solvents.

The content of the solvent is preferably 80 to 99.5% by mass, more preferably 90 to 99% by mass, based on the total mass of the coating liquid for forming a release layer.

That is, the total content of components other than the solvent (solid content) in the release layer forming coating liquid is preferably 0.5 to 20% by mass, more preferably 1 to 10% by mass, based on the total mass of the release layer forming coating liquid.

In order to improve the adhesion between the film and the release layer, pretreatment such as anchor coat, corona treatment, plasma treatment, or the like may be performed on the 1 st principal surface of the film before the release layer is provided.

< use >

The release film having the present film is preferably used as a release film (carrier film) for producing a ceramic green sheet. The ceramic green sheet produced using the release film can be preferably used for producing a ceramic capacitor in which the internal electrodes are required to be multilayered with the reduction in size and increase in capacitance.

The release film having the present film can also be used as a protective film for a dry film resist, a release film for process production, and the like.

The method for producing the ceramic green sheet using the release film is not particularly limited, and a known method can be carried out. Examples of the method for producing the ceramic green sheet include the following methods: the prepared ceramic slurry was applied to the surface of the release layer of the release film, and the solvent contained in the ceramic slurry was dried and removed.

The method of applying the ceramic slurry is not particularly limited, and a known method such as a method of applying a ceramic slurry in which ceramic powder and a binder are dispersed in a solvent by a reverse roll method and removing the solvent by heating and drying can be applied. The binder is not particularly limited, and examples thereof include polyvinyl butyral. The solvent is also not particularly limited, and examples thereof include ethanol and toluene.

Examples

The present invention will be described in more detail with reference to examples. The materials, the amounts used, the ratios, the contents of the treatments and the treatment steps shown in the following examples can be appropriately changed without departing from the gist of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. Unless otherwise specified, "part(s)" and "%" are based on mass.

[ example 1]

< extrusion Molding Process >

Particles of polyethylene terephthalate were produced using a titanium compound (citric acid chelated titanium complex, VERTEC AC-420, manufactured by Johnson Matthey PLC) described in Japanese patent No. 5575671 as a polymerization catalyst. The obtained pellets were dried to a water content of 50ppm or less, and then charged into a hopper of a twin-screw kneading extruder disclosed in Japanese patent No. 6049648, followed by melting at 280 ℃ and extrusion. After passing the melt (melt) through a filter (pore size 3 μm), it was extruded from a die into a cooling drum at 25 ℃ to obtain an unstretched film formed of polyethylene terephthalate. The extruded melt (melt) was closely adhered to a cooling drum by an electrostatic application method.

The melting point (Tm) of polyethylene terephthalate constituting the unstretched film was 258 ℃ and the glass transition temperature (Tg) was 80 ℃.

< longitudinal stretching step >

The above unstretched film was subjected to a longitudinal stretching step by the following method.

The preheated unstretched film was stretched in the longitudinal direction (transport direction) between 2 pairs of rollers having different peripheral speeds under the following conditions, to thereby produce a uniaxially oriented film.

(longitudinal stretching Condition)

Preheating temperature: 75 deg.C

Stretching temperature: 90 deg.C

Stretching ratio: 3.4 times of

Stretching speed: 1300%/second

< coating layer Forming step (particle-free layer Forming step and particle-containing layer Forming step) >

The following composition a-1 (composition for forming a particle-free layer) was applied to the cooling roll surface of a uniaxially oriented film (polyester substrate) stretched in the machine direction by a bar coater during the production of an unstretched film, the opposite surface was coated with composition B-1 (composition for forming a particle-containing layer), the formed coating film was dried with hot air at 100 ℃. At this time, the coating amounts of the compositions A-1 and B-1 were adjusted so that the thicknesses of the particle-containing layer and the particle-free layer to be formed became 60nm, respectively.

(compositions A-1 and B-1)

Compositions A-1 and B-1 were prepared by mixing the ingredients shown below. The prepared compositions A-1 and B-1 were subjected to filtration treatment using a Filter (F20, manufactured by Mahle Filter Systems Japan Corp) having a pore diameter of 6 μm and membrane deaeration (manufactured by 2x6 Radial Flow SuperPhbic, polypore company), and then the obtained compositions A-1 and B-1 were simultaneously coated on both sides of the uniaxially oriented membrane.

(composition A-1)

An acrylic resin (an aqueous dispersion of a copolymer obtained by polymerizing methyl methacrylate, styrene, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate and acrylic acid in a mass ratio of 59: 8: 26: 5: 2, at a solid content concentration of 25 mass%): 212 parts by mass

An anionic hydrocarbon surfactant (RAPISOL (registered trademark) a-90, di-2-ethylhexyl sulfosuccinate sodium manufactured by NOF CORPORATION, water diluted solution having a solid content of 1 mass%): 12 parts by mass

10 parts by mass of a carbodiimide-based crosslinking agent (an aqueous crosslinking agent for imparting a hydrophilic segment to a polycarbodiimide resin, manufactured by Nisshin Cott on Spinning Co., ltd., a solid content concentration of 40% by mass) 10 parts by mass of CARBODILITE (registered trademark) V-02-L2, nisshin Cott on Spinning Co., ltd.)

Water: 766 parts by mass (composition B-1)

Acid-modified olefin resin (ZAIKTHENE (registered trademark) NC, SUMITOMO SEIKA CHEMIC ALS co., ltd., product, aqueous dispersion of olefin resin, solid content concentration 28 mass%): 140 parts by mass

An anionic hydrocarbon surfactant (RAPISOL (registered trademark) a-90, di-2-ethylhexyl sodium sulfosuccinate, manufactured by NOF corporation 0N, water diluted solution having a solid content concentration of 1 mass%): 56 parts by mass

Particles (SNOWTEX (registered trademark) ZL, manufactured by Nissan Chemical Corporation, colloidal silica, aqueous dispersion with solid content concentration of 40 mass%): 11 parts by mass

Water: 793 parts of

< transverse stretching step >

The film subjected to the longitudinal stretching step and the coating layer forming step was stretched in the width direction using a tenter under the following conditions to produce a biaxially oriented film.

(conditions of transverse stretching)

Preheating temperature: 100 deg.C

Stretching temperature: 120 deg.C

Stretching ratio: 4.2 times of

Stretching speed: 50%/second

< Heat setting step >

The biaxially oriented film subjected to the transverse stretching step is heated under the following conditions using a tenter to thereby perform a heat setting step of heat setting the film.

(Heat-setting Condition)

Heat-setting temperature: 227 deg.C

Heat setting time: 6 seconds

< thermal relaxation step >

Next, the heat-set film is heated under the following conditions, thereby performing a heat relaxation step of relaxing the tension of the film. In the heat relaxation step, the film width is reduced as compared with the end of the heat setting step by reducing the distance (tenter width) between the gripping members of the tenter that grip both ends of the film. The following thermal relaxation rate Lr is determined from the formula Lr = (L1-L2)/L1 × 100 based on the film width L2 at the end of the thermal relaxation step relative to the film width L1 at the start of the thermal relaxation step.

(Heat-moderating Condition)

Heat relaxation temperature: 190 deg.C

Thermal relaxation rate Lr:4 percent

< Cooling Process and expansion Process >

The cooling step of cooling the heat-relaxed film was performed under the following conditions. In the cooling step, an expanding step is performed in which the width of the tenter is expanded to expand the film width more than that at the end of the heat relaxing step.

The following cooling rates were determined as follows: the residence time of the film from the cooling section of the drawing machine to the take-out is defined as a cooling time ta, and the cooling time ta is divided by a temperature difference Δ T (c) between the film surface temperature measured at the time of carrying in the film to the cooling section and the film surface temperature measured at the time of carrying out the film to the cooling section.

The following spreading factor Δ L is obtained from the formula of Δ L = (L3-L2)/L2 × 100, based on the film width L3 at the end of the cooling step relative to the film width L2 of the polyester film at the start of the cooling step.

(Cooling Condition)

Cooling rate: 2500 ℃/min

(expansion Condition)

Spreading factor Δ L:0.6 percent

< winding Process >

The film cooled in the cooling step was continuously cut along the transport direction at a position 20cm from both ends in the width direction of the film by using a trimmer, and both ends of the film were trimmed. Then, the film was subjected to extrusion processing (knurling) in a region of 10mm in the width direction from both ends of the film, and then the film was wound up with a tension of 40 kg/m.

In the above manner, a biaxially oriented film (polyester film) was produced in which a particle-free layer, a polyester base material, and a particle-containing layer were sequentially laminated. The obtained biaxially oriented film had a thickness of 31 μm, a width of 1.5m and a take-up length of 7000m. The thicknesses of the particle-free layer and the particle-containing layer of the obtained biaxially oriented film were measured by a scanning electron microscope (S-4800, manufactured by High-Technologies Corporation) after forming a cross section with a microtome, etching with Ar ions, pt deposition, and the thicknesses of the particle-free layer and the particle-containing layer were 60nm, respectively.

[ measurement of physical Properties of biaxially oriented film ]

The biaxially oriented film of example 1 was measured for the following properties.

< maximum protrusion height Sp, surface average roughness Sa >

The surface average roughness Sa and the maximum protrusion height Sp of the particle-free layer side surface and the particle-containing layer side surface of the biaxially oriented film were measured by the following methods.

The surface of the produced biaxially oriented film was measured using an optical interferometer (Vertscan 3300G LiLe, manufactured by Hitachi High-Technologies Corporation) under the following conditions, and then, analyzed with a built-in data analysis software (VS-Measure 5).

The average of the measurement values obtained by 5 measurements with the measurement position changed was used for the measurement of the surface average roughness Sa, and the average of the measurement values obtained by 5 measurements with the measurement position changed was used for the measurement of the maximum protrusion height Sp (denoted by P in the built-in data analysis software).

(measurement conditions)

Measurement mode: WAVE mode

Objective lens: 50 times of

Area of measurement: 186 μm X155 μm

< number of local protrusions >

The total number of protrusions having a height of more than 50nm was determined in the same manner as the maximum protrusion height Sp and the surface average roughness Sa, except that the measurement position was changed 100 times for the surface of the biaxially oriented film on the particle-free layer side.

< number of foreign matters >

The number of foreign matters on the surface of the particle-containing layer of the biaxially oriented film was measured by the following method.

A magnified image of the surface of the particle-containing layer 1 ten thousand times was observed with a scanning electron microscope (S-4800, manufactured by Hitachi High-Technologies corporation io n) to measure the number of foreign substances having a diameter of 1 μm or more present in a measurement area (measurement field) of 13 μm × 10 μm. This operation was performed in a total field of 40 fields where the measurement position was arbitrarily changed, and the total number of foreign matters (number of foreign matters) having a diameter of 1 μm or more was obtained.

Here, the foreign matter having a diameter of 1 μm or more means that the diameter of a circumscribed circle of the foreign matter is 1 μm or more.

Further, the observed foreign matter was analyzed for element distribution by EDS (Energy Dispersive X-ray Spectroscopy) analysis using the same analyzer, and it was judged as the oligomer (a low-molecular-weight by-product generated during polymerization of the polyester resin). The observed foreign matter was analyzed for its composition in detail by TOF-SIM (Time-of-Flight Secondary Ion Mass Spectrometry), and it was confirmed that the foreign matter was an oligomer.

< surface free energy >

The surface free energy of the surface on the side of the particle-free layer and the surface on the side of the particle-containing layer of the biaxially oriented film was measured by the following method.

A visual field contact angle meter (Kyowa Interface Science co., ltd., manufactured by dropsonster-501) was used to measure a contact angle 1 second after a droplet was attached to a surface of the produced biaxially oriented film on the particle-free layer side or the particle-containing layer side by dropping the droplet under a condition of 25 ℃. As the liquid droplets, 2. Mu.L of purified water, 1. Mu.L of diiodomethane and 1. Mu.L of ethylene glycol were used, and the surface free energy was calculated by Kitazaki and Hata methods based on the respective contact angles measured.

The "surface free energy" obtained by the above method is the sum of the polar component and the hydrogen bond component of the surface free energy.

[ concave-convex Defect (evaluation 1) ]

< preparation of ceramic slurry >

Barium titanate powder (BaTiO) in the presence of zirconia beads ₃ (ii) a100 parts by mass of SAKAI CHEMICAL INDUSTRY co., ltd. product name "BT-03"), 8 parts by mass of polyvinyl butyral resin (SEKISUI CHEMICAL co., ltd. product name "S-LEC B K BM-2") as a binder, and 4 parts by mass of dioctyl phthalate (KANTO CHEMICAL co., inc., dioctyl phthalate Cical grade) as a plasticizer, a mixed solution of toluene and ethanol (mass ratio 6: 4) 135 parts by mass were mixed and dispersed with a ball mill, and the beads were removed to prepare a ceramic slurry.

< preparation and evaluation of sample for measurement of concave-convex Defect >

After the wound film roll of the biaxially oriented film was left to stand at normal temperature and normal humidity for one week, a release layer (thickness of 1 μm) was formed on the particle-free layer surface of the biaxially oriented film after standing to obtain a release film. Here, the release layer is produced by a method of forming a release layer using the release layer forming material described in example 1 of jp 2015-195291 a.

The ceramic slurry was applied to the surface of a release layer of a release film having a width of 250mm and a length of 10m so that the thickness of the film after drying with a die coater became 1 μm, and then dried with a dryer at 80 ℃ for 1 minute. The laminated film of the ceramic green sheet and the release film was irradiated with a fluorescent lamp from the release film side, and all the surfaces of the formed ceramic green sheet were visually inspected, and evaluation of the concave-convex defect was performed based on the following criteria.

A: the ceramic green sheet was found to have no irregularity defects

B: from 1 to 5 concave-convex defects were confirmed on the ceramic green sheet

C: 6 to 30 concave-convex defects were observed on the ceramic green sheet

D: 31 or more concave-convex defects were observed on the ceramic green sheet

[ concave-convex Defect (evaluation 2) ]

A laminated film prepared in the same manner as for the uneven defect (evaluation 1) was used, except that the biaxially oriented film after standing at normal temperature and humidity for 3 months was used, and the same evaluation as for the uneven defect (evaluation 1) was performed.

[ measurement of physical Properties of peeled film ]

Using the release film obtained in the above-described "uneven defect" (evaluation 1), the maximum protrusion height Sp, the surface average roughness Sa, and the number of local protrusions were measured on the release surface of the release film (the surface of the release layer opposite to the side not containing particles) in the same manner as in the measurement of the physical properties of the biaxially oriented film.

[ examples 2 to 7]

Compositions B-2 to B-7 were obtained by changing a part of the materials contained in composition B-1 to the following materials. The above-described various physical property measurements and evaluation of the concave-convex defects were carried out in the same manner as in example 1 except that any of the compositions B-2 to B-7 was used instead of the composition B-1.

(composition B-2)

The acid-modified olefin resin was changed to the following acrylic resin.

Acrylic resin (aqueous dispersion of copolymer obtained by polymerizing methyl methacrylate, styrene, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate and acrylic acid at a mass ratio of 59: 8: 26: 5: 2, solid content concentration: 25% by mass)

(composition B-3)

The acid-modified olefin resin was changed to the following polyurethane resin a.

Polyurethane resin A (HYDRAN (registered trademark) AP-40N, manufactured by DIC Corporation, polyester polyurethane aqueous dispersion, having a solid content concentration of 35 mass% adjusted to a solid content concentration of 25 mass% with water

(composition B-4)

The acid-modified olefin resin was changed to the following polyurethane resin B.

Polyurethane resin B (SUPERFLEX (registered trademark) 210, dks co.ltd. Manufactured by ester polyurethane aqueous dispersion, the solid content concentration was adjusted to 35 mass% to 25 mass% with water)

(composition B-5)

The acid-modified olefin resin was changed to the following polyurethane resin C.

Polyurethane resin C (ADEKA BONTIGHTER (registered trademark) HUX-370, manufactured by ADEKA CORPORATION, polyurethane aqueous dispersion adjusted to a solid content concentration of 25% by mass with water

(composition B-6)

The acid-modified olefin resin was changed to the following PVA resin.

PVA resin (Kuraray Poval (registered trademark) PVA-117H, manufactured by Kuraray Co., ltd., aqueous PVA solution, solid content concentration 25% by mass)

(composition B-7)

The acid-modified olefin resin was changed to the following NBR (acrylonitrile butadiene resin) resin.

NBR resin (Nipol (registered trademark) LX-407C5, manufactured by Zeon Corporation, acrylonitrile butadiene rubber aqueous dispersion, solid content concentration was adjusted to 40 mass% with water to 25 mass% of solid content concentration)

[ examples 8 to 13]

A part of the materials contained in the composition A-1 was changed to the following materials to obtain compositions A-2 to A-7. The above-described various physical property measurements and evaluation of the concave-convex defects were carried out in the same manner as in example 1 except that any of the compositions a-2 to a-7 was used instead of the composition a-1.

(composition A-2)

The acrylic resin was changed to the following acid-modified olefin resin.

Acid-modified olefin resin (ZAIKKENE (registered trademark) NC, SUMITOMO SEIKA CHEMIC ALS CO., LTD., manufactured by aqueous dispersion of olefin resin, solid content concentration 28 mass% was adjusted to 25 mass% with water)

(composition A-3)

The acrylic resin was changed to the urethane resin a.

(composition A-4)

The acrylic resin was changed to the urethane resin B.

(composition A-5)

The acrylic resin was changed to the urethane resin C.

(composition A-6)

The acrylic resin was changed to the PVA resin.

(composition A-7)

The acrylic resin was changed to the NBR resin.

[ examples 14 to 16 ]

Using the compositions B-1, compositions B-8 to B-10 were prepared as follows. The above-described measurements of various physical properties and the evaluation of each concave-convex defect were carried out in the same manner as in example 1 except that any of the compositions B-8 to B-10 was used instead of the composition B-1.

(composition B-8)

NIPGEL (registered trademark) AZ-204 (manufactured by TOS0H SILICA CORPORATION) was added in the same amount as the solid content of SNOWTEX ZL.

(composition B-9)

NIPGEL (registered trademark) AZ-204 (manufactured by TOSOH SILICA CORPORATION) was added in an amount of 10 times the solid content of SNOWTEX ZL.

(composition B-10)

NIPGEL (registered trademark) AZ-204 (manufactured by TOSOH SILICA CORPORATION) was added in an amount of 20 times the solid content of SNOWTEX ZL.

[ example 17 ]

The above-described measurements of various physical properties and the evaluation of each concave-convex defect were carried out in the same manner as in example 15 except that the amount of the composition B-9 applied was adjusted so that the thickness of the particle-containing layer formed became 120 nm.

[ example 18 ]

The above-described various physical properties and evaluation of the concave-convex defects were carried out in the same manner as in example 1 except that the following composition a-8 was used instead of the composition a-1.

(composition A-8)

An acrylic resin (an aqueous dispersion of a copolymer obtained by polymerizing methyl methacrylate, styrene, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate, and acrylic acid at a mass ratio of 59: 8: 26: 5: 2, with a solid content concentration of 25 mass%): 141 parts by mass

Urethane resin B (SUPERFLEX (registered trademark) 210, dks co.ltd., ester-based polyurethane aqueous dispersion, solid content concentration 35 mass%): 38 parts by mass

An anionic hydrocarbon surfactant (RAPISOL (registered trademark) a-90, sodium di-2-ethylhexyl sulfosuccinate, manufactured by NOF CORPORATION, water diluted liquid having a solid content concentration of 1 mass%): 12 parts by mass

20 parts by mass of a carbodiimide-based crosslinking agent (an aqueous crosslinking agent for imparting a hydrophilic segment to a polycarbodiimide resin, manufactured by CARBODILITE (registered trademark) V-02-L2, nisshin Cotton Spinning Co., ltd., solid content concentration 40 mass%) (20 parts by mass)

Benzyl alcohol: 4 parts by mass of

Water: 785 parts by mass

[ example 19 ]

The above-described various physical properties were measured and the surface roughness defects were evaluated in the same manner as in example 18, except that the following composition B-11 was used instead of the composition B-1.

(composition B-11)

Organic particles a (MP 1000, manufactured by Soken Chemical & Engineering co., ltd., non-crosslinked acrylic acid particles, solid content 100 mass%): 8 parts by mass

Organic particles B (Nipol (registered trademark) UFN1008, manufactured by Zeon Corporation, polystyrene aqueous dispersion, solid content 20 mass%): 8 parts by mass

An acrylic resin (an aqueous dispersion of a copolymer obtained by polymerizing methyl methacrylate, styrene, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate and acrylic acid in a mass ratio of 59: 8: 26: 5: 2, at a solid content concentration of 25 mass%): 141 parts by mass

Benzyl alcohol: 4 parts by mass of

Water: 769 parts by mass

Comparative example 1

The above-described measurements of various physical properties and the evaluation of each uneven defect were carried out in the same manner as in example 1 except that the particle-free layer was not formed on the other surface of the polyester base material.

In addition, a release layer is formed on the surface of the polyester substrate on the side opposite to the particle-containing layer.

Comparative example 2

In example 1, the acrylic resin contained in composition a-1 was changed to aqueous polyester dispersion Aw-1 described in international publication No. 2017/199774 to obtain composition C-1. The above-described various physical property measurements and evaluation of the concave-convex defects were carried out in the same manner as in example 1 except that the composition C-1 was used instead of the composition a-1.

In table 1, "surface E" means "surface free energy".

As shown in table 1, when the release films obtained by storing the polyester films (biaxially oriented polyester films) of examples 1 to 17 according to the present invention for a long period of time were used for producing ceramic green sheets, the generation of concave-convex defects could be suppressed as compared with comparative examples 1 and 2.

As is clear from comparison of examples 1 to 7, when the non-polyester resin contained in the particle-containing layer is at least one resin selected from the group consisting of acrylic resins, urethane resins, and olefin resins, the concave-convex defect of the ceramic green sheet can be further suppressed (examples 1 to 5).

As is clear from comparison of examples 3 to 5, if the surface of the particle-containing layer on the side opposite to the polyester substrate has a surface free energy of 30 to 45mJ/m ² The concave-convex defects of the ceramic green sheet can be further suppressed (examples 3 and 4).

As is clear from the comparison of examples 1,8 to 13, 18 and 19, if the non-polyester resin contained in the particle-free layer is at least one resin selected from the group consisting of acrylic resins, urethane resins and olefin resins, the concave-convex defect (evaluation 1) of the ceramic green sheet can be further suppressed (examples 1,8 to 11, 18 and 19).

As is clear from comparison of examples 9 to 11, the surface free energy of the surface on the opposite side of the polyester substrate without the particle layer was 30 to 45mJ/m ² Then, the concave-convex defect of the ceramic green sheet (evaluation 2) can be further suppressed (examples 9 and 10).

As is clear from comparison between example 1 and examples 14 to 17, when the maximum projection height Sp of the surface of the particle-containing layer on the side opposite to the polyester substrate is 10 to 1500nm, the concave-convex defect of the ceramic green sheet can be further suppressed (examples 1, 14 to 16).

When the acrylic resin and the urethane resin were used together to form the particle-free layer (examples 18 and 19), the number of local protrusions of the release layer was 0 (no local protrusions were observed), and it was confirmed that the release layer was particularly preferable.

Description of the symbols

1-polyester film, 12-particle-containing layer, 14-polyester substrate, 16-particle-free layer.

Claims

1. A polyester film having in order:

a particle-containing layer containing particles;

a polyester substrate substantially free of particles; and

a particle-free layer substantially free of particles,

forming a release layer on a surface of the particle-free layer on the opposite side to the polyester substrate for producing a release film,

the particle-free layer contains a non-polyester resin other than a polyester resin.

2. The polyester film according to claim 1,

the release film is used for manufacturing a ceramic green sheet.

3. The polyester film according to claim 1 or 2,

the non-polyester resin contained in the particle-free layer is at least one resin selected from the group consisting of acrylic resins, polyurethane resins, and olefin resins.

4. The polyester film according to claim 1 or 2,

5. The polyester film according to claim 4,

6. The polyester film according to claim 1 or 2,

when 100 different portions of the surface of the particle-free layer on the side opposite to the polyester base material were measured with an optical interferometer in a measurement area of 186 μm × 155 μm per 1 portion, the total number of protrusions having a height of more than 50nm was 40 or less.

7. The polyester film according to claim 1 or 2,

8. The polyester film according to claim 1 or 2,

the maximum protrusion height Sp of the surface of the particle-free layer on the side opposite to the polyester base material is 1 nm-30 nm, and

the maximum protrusion height Sp of the surface of the particle-containing layer on the side opposite to the polyester base material is 10 nm-1500 nm.

9. The polyester film according to claim 1 or 2,

the thickness of the particle-free layer and the thickness of the particle-containing layer are each 1nm to 500nm.

10. The polyester film according to claim 1 or 2,

the surface of the particle-containing layer on the side opposite to the polyester base material had a surface free energy of 30mJ/m ² ～45mJ/m ² 。

11. The polyester film according to claim 1 or 2,

the thickness of the polyester film is less than 40 mu m.

12. A release film having the polyester film of any one of claims 1 to 11 and a release layer disposed on a surface of the particle-free layer opposite to the polyester substrate.

13. The release film according to claim 12,

when 100 different portions of the surface of the peeling layer on the side opposite to the particle-free layer were measured using an optical interferometer with a measurement area of 186. Mu. M.times.155. Mu.m per 1 portion, the total number of protrusions having a height of more than 50nm was 40 or less.

14. The release film according to claim 12,

the maximum protrusion height Sp of the surface of the particle-containing layer on the side opposite to the polyester base material is 10 nm-1500 nm, and

the maximum protrusion height Sp of the surface of the release layer opposite to the particle-free layer is 1nm to 30nm.